How to Build a V-Twin Motorcycle Engine

Written by don bowman
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Rebuilding a V-Twin engine is not difficult and can be done at home for the most part. This is the procedure for a Harley Davidson with high mileage or a cylinder upgrade to a bigger bore. The gas tank, horn, exhaust manifold and intake manifold should be off to start this procedure. Put the bike on a bike stand so the bike is level while you are working on it.

Skill level:
Moderately Challenging

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Things you need

  • Set of 3/8-inch drive sockets
  • 3/8-inch drive ratchet
  • Coat hanger
  • Wire cutter
  • Set of wrenches
  • Rubber mallet
  • Common screwdriver
  • Torque wrench
  • Teflon tape
  • Loctite compound
  • Rags
  • Piston pin remover and installer
  • Piston ring installer pliers
  • 2 hose clamps large enough to fit around piston.
  • 1 can STP oil treatment
  • 1 spray can of brake cleaner
  • Snap ring pliers

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Instructions

  1. 1

    Remove the spark plugs. The push rod covers and push rods will be labelled A, B, C and D. The labels can be seen as you are looking at the push rod side of the engine with A being the farthest left pushrod on the rear cylinder. Pry out the spring lock retainer on push rod A with a screwdriver and lift the bottom of the push rod cover up and hold it up with a piece of coat hanger. This will make it easier to work on the lifter.

  2. 2

    Rotate the engine so that the A push rod tappet moves down completely in its bore. Using a wrench on the top adjusting screw to hold it, loosen the bottom locknut and spin it with the fingers up to the base of the adjusting screw. Turn the adjusting screw all the way down into the bore.

  3. 3

    Remove the coat hanger and lift the push rod and cover out of the tappet and head. Mark it so that it goes in the same hole. That is important because the push rod has a wear pattern for that tappet and rocker assembly. If it is moved to another cylinder, it could cause rapid wear. Remove the oil lines on both cylinders.

  4. 4

    Remove the other push rods and covers the same way. Make sure the tappet, or lifter, is all the way down in the bore as far as it will go by turning the engine. Make sure the piston in the front cylinder is all the way down and remove the nuts holding the cylinder at the base. Use a rubber mallet and lightly tap the cylinder to break it loose and lift it straight up and off of the piston. Stuff rags into the hole around the connecting rod so nothing can fall inside and keep the rod from contacting the case.

  5. 5

    Move the piston all the way down in the next cylinder and do the same thing.

  6. 6

    Remove the snap rings holding the piston pin in (use the snap ring pliers). Using the piston pin remover, pull the pin from the pistons. Remove the bolts from the cylinder head and remove the cylinder head.

  7. 7

    Clean the combustion chamber with a wire brush, taking care not to touch the valve seats. Any scratches or marks on the valve seats will cause the valves to leak, which is not good. The valves would definitely need to be reseated if they got scratched.

  8. 8

    Pour water into the intake port and, while holding the cylinder head sideways, watch for water to pass the intake valve and drip out. If no water shows than that valve has a good seat. Do the exhaust valve the same way. If there are no leaks, the cylinder head should be all right, however make sure all the carbon is off the combustion chamber and look very close for cracks in the chamber, especially between the intake and exhaust valve. Lay a straight edge across the cylinder head and check for warpage. Check in several directions. Use a feeler gauge; as long as there is no more than .005 thousandth's warpage, it is OK.

  9. 9

    Take the cylinders to the Harley shop. Have a mechanic look at the cylinders and measure the inside diameter and the taper as well as wear on the cylinder walls and determine if the cylinders need to be bored or honed. They will match a new set of pistons to the bores and give you a new set of rings as well as cylinder bore gaskets and head gaskets. Have them inspect the head for cracks and the valves for seats and guide wear.

  10. 10

    Install the rings on the pistons, keeping the gaps 180 degrees apart. Hold the new pistons over the rods and push-start the piston pins into the rods. Install the piston pin tool and pull the pin through the rod and into the centre of the piston. Replace the cir clips or snap rings in both sides of the piston.

  11. 11

    Oil the piston rings and install the hose clamp over the rings and tighten just enough to compress the rings. Do not make them too tight since they must slip easily out into the cylinder. Turn the engine and raise the piston as high as it will go.

  12. 12

    Install the new cylinder base gasket. Make sure it is clean so there isn't anything to get compressed between it and the cylinder bore. Hold the cylinder over the piston and carefully lower it down on the piston and over the rings. Push it down where there is still room to take the hose clamps out and do so.

  13. 13

    Rotate the cylinder as necessary and push it down onto the studs. Install the nuts and tighten them in segments as you circle the jug. Tighten each nut a little more and then the next until they are down. Torque them to specifications. Raise the next piston as high as it will go and repeat the process.

  14. 14

    Make sure the cylinder heads are polished and ready to go and install the head gasket with a little oil on both sides of it. Install the cylinder heads and tighten the bolts in an X pattern a little at a time to seat it evenly. Torque to specifications. Wipe off all fingerprints.

  15. 15

    Start at push rod A to the far left on the rear cylinder and turn the engine until the tappet is all the way down in its bore. Put two new o-rings on the push rod tube --- one on the top and one on the bottom. Insert the push rod into the tube and carefully install the tube and rod into the top of the cylinder head. Make sure the o-ring is in place and feel for the push rod to fit into the upper rocker arm. While holding the push rod up, turn the adjusting screw up with a wrench to touch the push rod. Use the coat hanger and hold the tube up to make it easier to set the tappet clearance.

  16. 16

    Tighten the adjuster screw just enough that there is a very slight play up and down in the push rod and the rod can be turned with the fingers easily. Use a wrench to hold the adjuster screw and another wrench to tighten the locknut. Remove the coat hanger and lower the bottom of the push rod cover and make sure the bottom o-ring is in place. Insert the push rod spring clip holder.

  17. 17

    Make sure the next tappet is all the way down and repeat the process. Install the oil lines with Teflon tape and Loctite on the threads. Install the intake manifold with new gaskets and tighten. Install all the remaining parts in reverse order of their removal. Before the engine is started, it is wise to leave the plugs out and, using the starter, turn the engine over for 20 seconds at five-second intervals to get oil to the valve train.

Tips and warnings

  • A piston pin installer and extractor will be needed to install the piston on the rod. This tool can easily be made from a steel sleeve, some washers, nuts and a long 8-inch threaded rod. The easiest is to buy one since they are cheap.
  • Once the parts are disassembled, is a good time to dress them up to look good. Once assembled it is much more difficult.
  • The cylinders (after the work is done) can be cleaned and painted and the valve covers highly polished with Mothers or similar compounds. The cylinder heads are hard to get to after installation to do a great job. If they are not chrome, a little Mothers and some ultra fine wet and dry sandpaper will make the aluminium look just like chrome with very little work.
  • Clean the push rod covers and lightly sand with ultra fine sandpaper to remove any rust. If the chrome has come off anywhere, after sanding the rust off clean the area with alcohol. Get some chrome paint at the auto parts store and some clear topcoat in the aerosol cans. Tape off the area a lightly spray a few coats of the chrome over the area. After this dries lightly spray the clear over the chrome paint.

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